This invention relates to a process for molding high precision components. More particularly, the invention is directed to a method of fabricating components, e.g. fuel atomizers for gas turbine engines, using a process in which a mold pattern is created using multiple masking layers, a deep reactive ion etching process and photolithographic patterning techniques. The invention also is directed to reusable molds.
While the invention is directed to the art of molding high precision components, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications.
Generally, molding as a technology has existed for many years and has achieved a high degree of sophistication. Molding using silicon substrates, on the other hand, is a relatively new phenomenon. In the June, 1995 issue of the Journal of Microelectromechanical Systems, D. Sanders et al. reported the use of deep etched silicon molds in the article titled "Fabrication of metallic microstructures by electroplating using deep-etched silicon molds". However, it was a single pattern mold with only one etch step.
Further, it has been known to fabricate micromachined fuel atomizers from silicon (Si). The Si atomizers afford a high level of dimensional precision, which is lacking in both conventionally-machined and macrolaminated atomizers. However, under extremely erosive operational conditions, the Si atomizers suffer significant wear. While the development of hard coatings for these Si devices provided a solution for improving the wear resistance, there nonetheless remains a need for fabricating the complete atomizer from a material with high-temperature stability.
The fabrication of microelectromechanical systems (MEMS) devices from high-temperature materials has been hampered by the lack of processing technologies to effectively micromachine high-performance ceramics, like silicon carbide (SiC). While reactive ion etching (RIE) techniques have been developed to fabricate surface micromachined structures from SiC thin films, more complex three dimensional structures have not yet been realized. Excellent chemical stability/inertness of SiC significantly limits pattern delineation, depth and accuracy when utilizing etch processes.
Processes like Lithographie Galvanoformung Abformung (LIGA) provide the opportunity to fabricate micromachined devices from nickel (Ni), harnessing a material already used in the aerospace industry for its high-temperature characteristics and wear resistance in alloyed form. However, LIGA is not widely available and is often costly, driving the search for viable fabrication alternatives.
Other methods have sought to reduce cost by using UV (ultraviolet) sensitive photopolymers that allow molds of several hundred microns, but his method also suffers from lack of variation in the mold depth across the x-y plane of the mold.
The present invention contemplates a new and improved fabrication process for high precision components which resolves the above referenced difficulties and others.